The present invention relates generally to internal combustion engines and, more particularly, to cast iron cylinder or crank casings for such engines with at least a portion of the cylinder inner wall being hardened.
Cylinder or crank casings formed from cast iron are known generally in the prior art. In particular, German Pat. No. 3,029,215 shows such a cylinder casing wherein the inner wall of the cylinder has fine fluting thereon. This cylinder wall is partially hardened at the bottom regions of the grooves of that fluting. This shaping of the cylinder inner wall is intended to ensure favorable running-in properties, good adhesion of the lubricating oil film, and good wear resistance. However, this fine fluting does not impart rotational movement to the piston rings relative to the piston as the piston reciprocates through the cylinder.
It is an object of the present invention to provide a piston cylinder which provides secure sealing and even wear.
Another object is the provision of a cylinder which imparts rotational motion to piston rings with respect to the piston.
A further object is to provide a cylinder wall which ensures piston sealing and even piston ring wear by imparting rotational motion to the piston rings in response to reciprocating motion of the piston head.
These and other objects of the present invention are achieved by the provision of a cylinder means, for use in an internal combustion engine, having strip-shaped hardened zone means on its internal walls. These zone means are disposed obliquely to the cylinder generator lines and serve to impose rotational movement on the piston ring means as the piston head slides through the cylinder means.
The strip-shaped hardened zone means always remain somewhat raised after fine machining of the inner wall of the cylinder means. These zone means present a steep, tread-like guidance to the piston ring means so that the rings rotate relative to the piston during both stroke directions of the piston. Because of the varying pressure loading during the individual piston strokes, these rotational motions may be different in each case. The net result, however, is that the piston ring means are evenly loaded over their periphery.
The strip-shaped zone means can form straight or curved strips along the cylinder means inner wall. These strips may be continuous or formed from a series of discrete hardened points. The zone means may be evenly distributed over the inner periphery of the cylinder means wall and may make an angle of between 10.degree. and 30.degree. with respect to the generator lines of the cylinder inner wall. The zone means may extend into the stroke region of the first piston ring of each piston.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.